Method for generating a time-limited signal

ABSTRACT

Method for generating a time-limited signal.  
     In the previously known methods, the circuit arrangements for generating a time-limited signal continue to draw current even after the signal has been generated.  
     With the new method, the circuit arrangement draws no current after the time-limited signal has been generated.

BACKGROUND

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for generating a time-limited signal, in accordance with the preamble of claim 1.

[0003] 2. Description of the Related Technology

[0004] A method of this kind is known from the publication DE 100 24 980.9. After providing a supply voltage, an initialization signal (Power-on-Reset) is generated for a following circuit arrangement. A disadvantage is that the method calls for an elaborate circuit arrangement that requires a large chip surface and that the circuit arrangement continues to consume electric current after the reset signal has been generated.

[0005] In general, methods for generating a time-limited signal are used in particular by so-called “reset” or initialization signals” in order to set defined electrical parameters or initial states in circuit arrangements after applying a supply voltage. Another important application of signals of limited duration is the change of states while an electrical circuit arrangement is in operation. Furthermore, it is important to develop methods for circuit arrangements that should have a low operating current or consume little current in the quiescent state in order, for instance, to keep the discharge rate of a battery low. In particular in applications in motor vehicles with the 42 volt vehicle electrical system, it is important for these arrangements to consume little current even where there are high supply voltages.

SUMMARY OF THE INVENTION

[0006] The object of the present invention is to specify a method for generating a time-limited signal that reduces the current consumption in a circuit arrangement. Another object of the invention is to specify a circuit arrangement for performing the method that can be produced by simple means and at low cost.

[0007] The first of these objects is solved by the features of claim 1 while the solution for the second of these objects is demonstrated by the features of claim 12. Favorable modifications to the design are given in Subclaims.

[0008] Accordingly, the essence of the invention is to generate a time-limited signal in a circuit arrangement by means of a capacitive voltage divider and to reduce the flow of current in the circuit arrangement to zero after the signal has been generated. For this purpose, in order to generate a time-limited signal, at at least one signal output of a circuit arrangement, that has at least one first switching unit and one second switching unit each having an output and an input and a capacitive voltage divider with a first divider junction and a second divider junction, the circuit arrangement is put into a current-carrying state for just a limited period of time by applying the supply voltage and within this period of time a time-limited signal is fed to a signal output of the circuit arrangement. After applying the supply voltage, current flows from the first divider junction to the input of the first switching unit thereby discharging the first divider junction and during the discharging time the input of the second switching unit is activated by the output of the first switching unit and the second divider junction is charged by means of the output of the second switching unit and the time-limited signal is taken from a circuit junction within the circuit arrangement. The time-limited signal is determined here by the discharging time of the first divider junction and/or by the charging time of the second divider junction.

[0009] One advantage of the method is that the circuit arrangement consumes no further current after the time-limited signal has been generated. This allows a time-limited signal to be provided for further switching units without the initialization circuit increasing the current flow in the overall system after generation of the time-limited signal. The period over which current is input to the circuit arrangement is determined by the discharging times and the size of the capacitances of the capacitive voltage divider. Furthermore, within the period in which current is flowing in the circuit arrangement, it is possible to determine by the electrical parameters of the switching units the duration and rise behavior of the output signal. In addition, the duration of the output signal depends on the point at which the time-limited signal is output. Studies made by the applicant have shown that the method can be applied over a wide range of supply voltages, for instance between 3 and 60 volts, the maximum voltage depending on the electric strength of the components used in the circuit arrangement. Also, by disconnecting and reconnecting the circuit arrangement to the supply voltage, it is possible to generate several time-limited signals in succession. Moreover, by means of the voltage thresholds in the respective switching units, the time-limited signal can be generated reliably even at low supply voltages of, for example, 5 volts and lower and also when the supply voltage builds up slowly.

[0010] In a further development of the method, the second switching unit is activated by means of current from the first switching unit. This current is limited by a negative-feedback element in order to suppress overshoot and too rapid charging of the second divider junction. The limitation of the output current of the first switching unit can be performed either with a current source circuit or with a passive component such as a resistor

[0011] In another development of the method, the voltage at the second divider junction that is pulled towards the supply voltage level by the charging current of the second circuit arrangement is limited to a preset potential by means of a voltage-limiting element. With high supply voltages in particular, for instance voltages above 60 volts, capacitors with a much lower electric strength can be used between the first divider junction and the second divider junction. In this case, it is advantageous to limit the voltage by means of a diode structure, preferably by means of a Zener diode

[0012] In a further development of the method, current is caused to flow through a first current-controlled switch by means of the first divider junction within the first switching unit and current is caused to flow through a second divider junction by means of a second current-controlled switch within the second switching unit. In this case, it is advantageous to limit the output current of the second switch by a resistor Studies made by the applicant have shown that it is advantageous to feed out the time-limited signal by means of an additional driver transistor in order to avoid influencing the charging or discharging process between the two divider junctions. The driver transistor generates, for example, a time-limited current which can be transformed into a voltage signal by means of a resistor.

[0013] In another further development of the method, current is caused to flow through a first current mirror from the first divider junction within the first switching unit and current is caused to flow through the second divider junction by means of a second current mirror within the second switching unit. An advantage of the current mirror circuit is that, as opposed to the current-controlled switches, it has no passive components and in particular for small capacitances of the voltage divider it can be produced in a small size and at low cost. Furthermore, studies made by the applicant have shown that it is advantageous for one of the mirror circuits to be extended by means of an additional transistor to form a current bank in order to feed out the time-limited signal. In particular when using MOS transistors here, the current in the current mirrors is influenced only slightly. Furthermore, in a development of the method, the current mirror circuit can be combined with the circuit of the current-controlled switch.

[0014] Other studies made by the applicant have shown that it is of advantage when the capacitor between the reference potential and the first divider junction and the capacitor between the supply voltage and the second divider junction are formed by the parasitic capacitors at the input and the output respectively of the switching units. Since only the capacitor between the first divider junction and the second divider junction is provided in the form of a passive component, the circuit arrangement can be produced with a small surface area and at low cost.

[0015] In a further development of the invention, the time-limited signal is fed out preferably at the second divider junction by means of a capacitive element, such as a capacitor for example. In this case, the current consumption of the circuit arrangement can be reduced and the additional driver transistor for driving the output is omitted.

BRIEF DESCRIPTION OF THE FIGURES

[0016] The method according to the invention will now be explained with reference to several schematic examples of embodiment in conjunction with the drawings. The drawings show:

[0017]FIG. 1a a circuit arrangement with a capacitive circuit divider and two switching units, and

[0018]FIG. 1b the relationship between the rise in voltage at the input of the circuit arrangement and the time-limited signal at the output of the circuit arrangement of FIG. 1a, and

[0019]FIG. 2 a voltage-limiting element for protecting the circuit arrangement against overvoltage, and

[0020]FIG. 3 an embodiment of the circuit arrangement with two current-controlled switches in the switching unit, and

[0021]FIG. 4 an embodiment of the circuit arrangement with two current mirrors in the switching units, and

[0022]FIG. 5 an embodiment of the circuit arrangement in which the input and output capacitance respectively of the current mirrors form a part of the capacitive voltage divider.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The circuit arrangement SA shown in FIG. 1a generates a time-limited signal S1 at an output A1 by applying a supply voltage VS. After applying this supply voltage, a current IE1 flows through the circuit arrangement SA over a period of time ZG in which the time-limited signal S1 is fed in the output A1. After signal S1 has been generated, the circuit arrangement SA consumes no further current The relationship in terms of time between the applying of the supply voltage VS and the rise of voltage UE1 at the input E1, as well as the current IE flowing into the input E1 and the signal S1 is shown schematically in FIG. 1b in a voltage/time chart and in a current/time chart.

[0024] Here follows an explanation of the design of the circuit arrangement SA. The circuit arrangement SA has an input E1 to which a supply voltage VS is applied. The input E1 is connected to a series circuit comprising a capacitor C3, a capacitor C2 and a capacitor C1 which is connected to the reference potential. The series circuit of capacitors C1 to C3 forms a capacitive voltage divider with a first divider junction K1 between the capacitor C1 and the capacitor C2 and a second divider junction K2 between the capacitor C2 and the capacitor C3. Furthermore, the circuit arrangement SA has a first switching unit SE1 which is connected to the reference potential and a second switching unit SE2 which is connected to the input E1. Additionally, the first divider junction K1 is connected to an input STE1 of the first switching unit SE1 Also, the first switching unit SE1 has an output STA1 which is connected to an input STE2 of the second switching unit SE2 via a current-limiting element IB1 that is connected in series. In addition, the switching unit SE2 has an output STA2 which is connected to the second divider junction K2. Moreover, the first switching unit SE1 is connected to the output A1 by means of a signal output.

[0025] In the following, the mode of operation of the circuit arrangement SA will be explained with reference to the charts shown in FIG. 1b. After the supply voltage VS has been applied, the supply voltage UE1 at input E1 of the circuit arrangement SA rises slowly up to the level of the supply voltage VS, as shown in FIG. 1b, the difference in time between the level of the supply voltage VS and the rise of voltage UE1 being mainly due to parasitic resistances and inductances. Current then flows through the capacitive voltage divider and the capacitors C1 to C3 and the divider junctions K1 and K2 are charged. Via the divider junction K1, current flows at the input of the switching unit SE1 while the divider junction K1 is discharged. Subsequently, current flows from the switching unit SE1 through the input STE2 of the switching unit SE2 via the current-limiting element IB1, while the switching unit SE2 causes current to flow via the output STA2 to the divider junction K2, which then charges. Because of the current flowing through the circuit arrangement SA, the signal S1 is fed to the output A1 for a time Z1, as shown in FIG. 1b, after a time Z0 which is determined primarily by the divider ratios of the voltage divider and the voltage threshold values of the switching unit SE1. After a further time Z2, in which the signal S1 is no longer fed to the output A1, current ceases to flow through the circuit arrangement SA. The time ZG, in which current flows through the switching unit SE1, is determined primarily by the discharge time of the divider junction K1. This discharge time is dependent on the magnitude of the further charging of the divider junction K2 and the current flowing through the input STE1 or alternatively by voltage thresholds within the switching unit SE1.

[0026] An advantage of the circuit arrangement SA is that the circuit arrangement SA draws current only within the period of time ZG. The time ZG is determined here by the effective RC times of the circuit arrangement SA and the magnitudes of the currents that flow through the two divider junctions K1 and K2. Furthermore, either a resistor or a current source can be used as negative-feedback element IB1 in the circuit arrangement SA in order to limit the current.

[0027] In the circuit arrangement SA for generating the time-limited signal S1, as shown in FIG. 2, the voltage at the divider junction K2 is limited by means of a voltage-limiting element VB1 which is connected to the reference potential. Furthermore, the circuit arrangement SA has another output A2 at which a time-limited signal S2 can be fed out, for instance by means of a capacitive element, preferably a capacitor.

[0028] The explanations given below are in addition to what has been said with reference to the drawings of FIG. 2. Furthermore, above the voltage threshold of the voltage-limiting element VB1, which takes the form of a Zener diode for example, the current is diverted from the divider junction K2 and flows to the reference potential, which means that further charging of the divider junction K2 is suppressed. Once charging of the divider junction K2 has been completed, the divider junction K1 is no longer charged by the divider junction K2 and is therefore discharged faster by the switching unit SE1. Consequently, the time needed for the switching unit SE1 to trigger the switching unit SE2 is reduced. As a result, the time Z2 in particular and the time ZG, in which a time-limited signal S1 is fed to the output A1 and in which the current IE flows through the circuit arrangement SA, is reduced

[0029] An advantage of the voltage-limiting element VB1 is that, especially at high supply voltages, the capacitor C2 need have only a low electric strength. Furthermore, the time ZG, in which the current IE flows through the circuit arrangement, can be changed by the voltage threshold of the voltage-limiting element VB1, the time ZG being proportional to the level of the voltage threshold of the voltage-limiting element VB1. Furthermore, when the time-limited signal S2 is fed out at output A2, the output A1 on the switching unit SE1 can be omitted.

[0030] In the circuit arrangement SA shown in FIG. 3, the time-limited signal S1 is generated by the two switching units SE1 and SE2 by means of a first current-controlled switch IS1 and a second current-controlled switch IS2. Here, the output A1 is triggered with the signal S1 from switch IS1 by means of a driver transistor T7, provided the output A1 is connected via a resistance element to a potential that is above the reference potential. In addition, the output current of the switch IS2 is limited by means of an element IB2.

[0031] The circuit arrangement in the two switching units SE1 and SE2 will now be described in more detail. The input STE1 is connected to a resistor R1 that is connected to the reference potential, and to the control input of a transistor T6, and to the control input of the driver transistor T7. Also, the source of the transistor T6 and the source of the transistor T7 are each connected to the reference potential. The drain of the transistor T6 is connected to the output STA1 of the switching unit SE1 Furthermore, in the second switching unit SE2 the input STE2 is connected to a resistor R2, that is connected to the power supply VS, and to the control input of the transistor T8. The source of the transistor T8 is connected to the input E1. The drain of the transistor T8 is connected to the output STA2 via the current-limiting element IB2 which is provided, for example, in the form of a resistor.

[0032] The mode of operation of the two current-controlled switches IS1 and IS2 will now be explained below. After the supply voltage VS has been applied to the input E1, current flows through the resistor R1 in accordance with the potential at the divider junction K1, and consequently the transistor T6 or T7 respectively becomes conductive above the relevant threshold voltage due to the voltage drop across the resistor R1. Subsequently, current flows from transistor T7 to the output A1 Furthermore, current flows from the input E1 via the resistor R2. If the magnitude of the voltage drop across the resistor R2 is greater than the threshold voltage at transistor T8, current flows at the junction K2 via the output STA2. When the voltage at resistor R1 drops below the threshold voltage of the transistor T6 or T7 respectively, no current flows through the resistor R2 and at output A1, i.e. the junction K2 is no longer charged via the output STA2.

[0033] An advantage of the particular design of the circuit arrangement SA is that in place of the first switch IS1 the second switch IS2 can also be connected to the output A1 via an additional driver transistor in order to thereby provide a time-limited signal for a following circuit stage.

[0034] In FIG. 4, the time-limited signal S1 is generated by the two switching units SE1 and SE2 by means of a first current mirror SPI and a second current mirror SP2. Signal S1 is sent here to the output A1 in the circuit arrangement SA from the current mirror SP1 via a driver transistor T3, provided a potential that is greater than the reference potential has been placed on output A1 via a resistance element. Furthermore, to limit the voltage at the capacitor C2, the divider junction K2 is connected to the voltage-limiting element VB1. The circuit arrangement in the two switching units SE1 and SE2 will now be described below.

[0035] The input of the first switching unit SE1 is connected to a NMOS transistor T1 that is connected as a diode, i.e. the drain and the gate of the transistor T1 are connected together. The source of the transistor T1 is connected to the reference potential and to the source of a NMOS transistor T2 and to the source of a NMOS transistor T3. The gate of the transistor T1 is connected to the gate of the transistor T2 and to the gate of the transistor T3. Furthermore, the drain of the transistor T2 is connected to the output STA1 of the switching unit. Also, the drain of the transistor T3 is connected to the output A1. In the switching unit SE2, the source of a NMOS transistor T4 and the source of a PMOS transistor T5 are connected to the input E1. Furthermore, the drain of the transistor T5 is connected to the output STA2 of the switching unit SE2. Also, the gate of the transistor T5 is connected to the gate of the transistor T4, to the drain of the transistor T4, and to the input STE2 of the switching unit SE2.

[0036] The mode of operation of the circuit arrangement SA will now be described below. After the supply voltage VS has been applied to the input E1, the transistor T1 becomes conductive. If the voltage at the gate of the transistor T1 rises above the threshold voltage of the transistor T2 or of transistor T3 respectively, both transistors T2 and T3 respectively become conductive. Subsequently, current flows from the transistor T3 to the output A1 Furthermore, the current IE flows from the input E1 through the transistor T2 and the transistor T4. If the magnitude of the voltage drop across the transistor T4 is greater than the threshold voltage at the transistor T5, the junction K2 receives current via the output STA2. If the voltage at the transistor T1 drops below the threshold voltage of the transistor T2 or T3 respectively, current ceases to flow at the output A1 and through the transistor T4, i.e. the junction K2 is no longer charged via the output STA2.

[0037] An advantage of the current mirror arrangement is that this design of the circuit arrangement SA requires only a small chip surface and can be manufactured at an especially low cost. Furthermore, the circuit arrangement SA draws little current on account of the two current mirror circuits, the transistors of which can be activated, for example, in the subthreshold range. Together with small capacitances in the voltage divider, it is possible here to generate long time-limited signals.

[0038] In FIG. 5, the time-limited signal S2 is generated by the two switching units SE1 and SE2 by means of the two current mirrors SP1 and SP2. The capacitors C1 and C3 are replaced here by the input capacitances and output capacitances respectively of the two switching units SE1 and SE2 and hence by the two current mirrors SP1 and SP2. In the following, reference will be made to the explanations concerning the drawings relating to FIG. 4, although in contrast to the circuit arrangement shown in FIG. 4 the voltage-limiting element VB1 is connected to the divider junction K2 and, by feeding out the signal S2 at the output A2, both the output A1 and the transistor T3 are omitted.

[0039] The mode of operation will now be explained. Because of the design of the capacitive circuit divider using the input capacitance of the switching unit SE1 and the output capacitance of the switching unit SE2, the total capacitance within the circuit arrangement is small and the current that flows in the input E1 after the supply voltage VS has been applied is very small since the charging and discharging currents are also small. In addition, the surface area of the transistors can be reduced considerably. In total, the chip area is reduced. Furthermore, due to the voltage-limiting element VB1 the demands with respect to electric strength are reduced. In particular with high supply voltages and technologies that provide only capacitors with a low specific capacitance, the integration capability of the circuit arrangement is enhanced.

[0040] An advantage of the method is that the circuit arrangement can be designed with both bipolar and MOS transistors. In addition, the method and the circuit arrangement can be applied over a wide range of supply voltages. Furthermore, by disconnecting from the supply voltage and then reconnecting to it, several successive time-limited signals can be generated, while the circuit arrangement draws no current after the time-limited signal has been generated. 

What is claimed is:
 1. Method for generating a time-limited signal (S1) at least at one signal output (A1) of a circuit arrangement (SA) that has at least a first switching unit (SE1) and a second switching unit (SE2) each having an output (STA1, STA2) and an input (STE1, STE2) and a capacitive voltage divider (C1, C2, C3) with a first divider junction (K1) and a second divider junction (K2), wherein the circuit arrangement (SA) creates a current-carrying condition for a specific period of time (Z1) as a result of applying the supply voltage (VS) and within this time (Z1) a time-limited signal (S1) is fed to a signal output (A1) of the circuit arrangement (SA) in that current flows from the first divider junction (K1) to the input (STE1) of the first switching unit (SE1) while at the same time the first divider junction (K1) discharges, and within the discharging time the input (STE2) of the second switching unit (SE2) is activated by the output (STA1) of the first switching unit (SE1) and the second divider junction (K2) is charged via the output (STA2) of the second switching unit (SE2), and at a circuit junction within the circuit arrangement (SA) the time-limited signal (S1) is fed out, and the time-limited signal (S1) is determined by the discharging time of the first divider junction (K1) and/or by the charging time of the second divider junction (K2)
 2. Method in accordance with claim 1, wherein the second switching unit (SE2) is activated by the first switching unit (SE1) by means of a current that is limited by a negative-feedback element (IB1).
 3. Method in accordance with claim 2, wherein the limiting of the current is performed by means of a passive component, preferably a resistor (R3).
 4. Method in accordance with claim 1, wherein the potential of the second divider junction (K2) is limited by a voltage-limiting element (VB1).
 5. Method in accordance with claim 4, wherein the limiting of the potential is performed by means of a diode structure, preferably a Zener diode.
 6. Method in accordance with claim 5, wherein the first divider junction (K1) is supplied with current from the first switching unit (SE1) via a first current-controlled switch (IS1) and the second divider junction (K2) is supplied with current from the second switching unit (SE2) via a second current-controlled switch (IS2). 7 Method in accordance with claim 1, wherein the first divider junction (K1) is supplied with current from the first switching unit (SE1) via a first current-controlled switch (IS1) and the second divider junction (K2) is supplied with current from the second switching unit (SE2) via a second current-controlled switch (IS2).
 8. Method in accordance with claim 6, wherein the output current of the second switch (IS2) is limited by a current-limiting element (IB2). 9 Method in accordance with claim 7, wherein the output current of the second switch (IS2) is limited by a current-limiting element (IB2).
 10. Method in accordance with claim 6, wherein a time-limited current is generated in order to generate the time-limited signal (S1) from the first switch (IS1) via a driver transistor (T7)
 11. Method in accordance with claim 5, wherein the first divider junction (K1) is supplied with current from the first switching unit (SE1) via a first current mirror (SP1) and the second divider junction (K2) is supplied with current from the second switching unit (SE2) via a second current mirror (SP2).
 12. Method in accordance with claim 1, wherein the first divider junction (K1) is supplied with current from the first switching unit (SE1) via a first current mirror (SP1) and the second divider junction (K2) is supplied with current from the second switching unit (SE2) via a second current mirror (SP2).
 13. Method in accordance with claim 11, wherein at least the current mirror (SP1, SP2) that activates the voltage-limiting element (VB1) is extended to form a current bank in order to generate the time-limited signal (S1). 14 Method in accordance with claim 11, wherein the generation of the current in the circuit arrangement is performed from a combination of a current-mirror circuit and a current-controlled switch.
 15. Method in accordance with claim 11, wherein two capacitances (C1, C3) of the capacitive voltage divider are formed from parasitic capacitances of the switching units (SE1, SE2).
 16. Method in accordance with claim 15, wherein the time-limited signal (S1) is fed out at the second divider junction (K2) by means of a capacitive element, preferably a capacitor.
 17. Method in accordance with claim 1, wherein the time-limited signal (S1) is fed out at the second divider junction (K2) by means of a capacitive element, preferably a capacitor. 18 Circuit arrangement (SA) for performing the method for generating a time dependent signal with a first switching unit (SE1) that has a current input (STE1) and current output (STA1), a second switching unit (SE2) that has a current input (STE2) and current output (STA2), a current-limiting element (IB1), a first capacitive element (C1), a second capacitive element (C2), a third capacitive element (C3) and an output (A1), wherein the three capacitive elements (C1, C2, C3) are connected in series as capacitive voltage divider, the current input (STE1) of the first switching unit (SE1) is connected to a first divider junction (K1) of the capacitive voltage divider, the current output (STA2) of the second switching unit (SE2) is connected to a second divider junction (K2) of the capacitive voltage divider, the current output (STA1) of the first switching unit (SE1) is connected to the current input (STE2) of the second switching unit (SE2), and the signal output (A1) of the circuit arrangement (SA) is connected to an output (A) of the first switching unit (SE1).
 19. Circuit arrangement in accordance with claim 18, wherein a current-limiting element (IB1) is connected to the current output (STA1) of the first switching unit (SE1) and the current input (STE2) of the second switching unit (SE2).
 20. Circuit arrangement in accordance with claim 19, wherein a voltage-limiting element (VB1) is connected to the second divider junction (K2).
 21. Circuit arrangement in accordance with claim 18, wherein a voltage-limiting element (VB1) is connected to the second divider junction (K2).
 22. Circuit arrangement in accordance claim 18, wherein the first switching unit (SE1) comprises at least a first current-controlled switch (IS1) and the second switching unit (SE2) comprises at least a second current-controlled switch (IS2), where the two switches (IS1, IS2) preferably have a grounded-emitter circuit or a grounded-source circuit, and the first current-controlled switch (IS1) is connected to the signal output (A1) of the circuit arrangement (SA) via a driver transistor (T7) and the second switch (IS2) is connected to the divider junction (K2) via a current-limiting element (IB2)
 23. Circuit arrangement in accordance claim 20, wherein the first switching unit (SE1) comprises at least a first current-controlled switch (IS1) and the second switching unit (SE2) comprises at least a second current-controlled switch (IS2), where the two switches (IS1, IS2) preferably have a grounded-emitter circuit or a grounded-source circuit, and the first current-controlled switch (IS1) is connected to the signal output (A1) of the circuit arrangement (SA) via a driver transistor (T7) and the second switch (IS2) is connected to the divider junction (K2) via a current-limiting element (IB2)
 24. Circuit arrangement in accordance with claim 18, wherein the first switching unit (SE1) comprises at least a first current mirror (SP1) and the second switching unit (SE2) comprises at least a second current mirror (SP2), and at least one current mirror (SP1, SP2) is connected to the signal output (A1) of the circuit arrangement (SA) via a driver transistor (T3).
 25. Circuit arrangement in accordance with claim 19, wherein the first switching unit (SE1) comprises at least a first current mirror (SP1) and the second switching unit (SE2) comprises at least a second current mirror (SP2), and at least one current mirror (SP1, SP2) is connected to the signal output (A1) of the circuit arrangement (SA) via a driver transistor (T3). 